This invention relates to a method for determining the concentration of at least two salts in a liquid medium, wherein said salts exhibit different affects on X-ray absorption and sound velocity in the medium. In a preferred embodiment, this method determines the respective concentrations of (a) an ammonium or alkali metal hydroxide and (b) an ammonium or alkali metal halide, sulfite, sulfate, hypochlorite or hypobromite by measurement of sound velocity and X-ray absorption.
It is conventional in the prior art to determine the concentration of a salt in a liquid medium by one of a variety of "wet analysis" techniques. Titration methods for hydroxides are well established. Likewise, methods for analysis of halides via titration with silver nitrate are conventional. Specific titrimetric methods for determining concentration of many other compounds are known. See H. H. Willard et al, Instrumental Methods of Analysis, D. Van Nostrand Company Inc. (1965). However, such methods require automated or manual sample handling and are relatively slow.
Sound velocity measurements have recently emerged as a means for determining the concentration of solutes present in aqueous solutions. U.S. Pat. No. 3,648,513 describes the use of sound velocity measurements to determine the concentration of sodium chloride in underground bodies of water. Mokrousova et al, Khim. Volokna, 5, pp. 66-7 (1978), describe the use of sound velocity measurements to measure NaOH concentration. However, sound velocity measurements cannot accurately determine the concentration of more than one salt present in the aqueous solution wherein two or more of the salts affect the sound velocity.
Absorption of low-energy X-ray radiation has been used in the art to determine concentrations of certain materials. H. F. Liebhafsky et al, X-Rays, Electrons and Analytical Chemistry, pp. 127-170, Wiley-Interscience (1972). This analytical technique also does not permit accurate determination of concentrations in multicomponent solutions where more than one component abosrbs X-rays.